This invention relates to lighter than air balloons. In another aspect, this invention relates to a novel substantially balloon for use as a toy or in advertising which will remain buoyant for an indefinite period of time in excess of about one year with a potential maximum lifetime exceeding several years, e.g., at least 30 years.
Conventionally small toy or advertising balloons are made by filling an elastomeric material with a helium containing gas. Such lighter than air balloons have been commonly used and sold for many years at fairs, circuses, restaurants and shopping centers and the like, where helium is available to fill the balloons shortly before use or sale. Thus, it is commonly known that such balloons invariably lose their buoyancy within a matter of a few hours or few days at most, as the result of helium losses by diffusion through the elastomeric envelope material. Therefore, such balloons have not been marketed through conventional channels of commerce because of the limited shelf life amounting to only a matter of days. The limited lifetime of such balloons as disappointed millions of children and has prevented the sale of the buoyant balloons by the vast majority of merchants who do not have the resources to fill the balloons as they are sold and who cannot afford the inevitable losses which are associated with the short shelf life of the product.
Larger aeronautical balloons have been made which have relatively long buoyant lifetimes. In general, as the volume of a balloon is increased then it becomes easier to design relatively impermeable envelope materials, because the larger volume of gases will support the relatively thick envelope which is necessary to provide impermeability for the lighter than air gases. Much work has been conducted in the field of large aeronautical balloons to devise composite envelope materials which are relatively impermeable to gases and provide great strength. For example, German Pat. No. 217,110 discloses an envelope material made by gluing galvanic metal paper to cotton, linen or silk cloth. German Pat. No. 219,440 discloses a balloon envelope material made by sandwiching cloth between sheets of aluminum and copper. German Pat. No. 224,521 discloses a balloon envelope material made by bonding corrugated sheets of metal, glass or organic material to fabrics. German Pat. No. 227,150 discloses balloon envelope materials which are made less permeable by deposition of a metallic mirror finish thereto in a reducing bath. German Pat. No. 515,083 discloses balloon envelope material made by gluing cellulose skin to metal foil to mutually increase the strength of the layers. U.S. Pat. No. 1,793,075 discloses gas envelope material made by combining layers of rubberized fabric, rubber cement and metal leaf. U.S. Pat. No. 1,801,666 discloses a gas envelope material made by coating a sheet of aluminum with a tacky rubber isomer, baking the resulting composite to form an enamel coat and adhering the resulting sheet to fabric, paper, rubber or leather. None of the above patents disclose methods by which the composite sheet materials can be fashioned into balloon envelopes other than by the conventional methods of sewing, taping and joint caulking which are only suitable for the very large aeronautical balloons which have a substantially large wall thickness of the envelope material.
As is apparent from the above discussion based upon relatively old patents, most of the research in balloon technology occurred before the World War II era and was related to aeronautical type balloons for transmitting men and/or equipment. In these patents, the words "gastight" or "gasproof" or "impermeable" are used in a loose sense to describe virtually all nonwoven or nonporous materials. For example, U.S. Pat. No. 2,730,626 described rubber material as "gastight material" whereas such materials invariably have measurable permeability to lighter than air gases. Similarly, U.S. Pat. No. 1,449,748 describes rubber impregnated fabric coated with drying oil and aluminum powder as "gasproof" where "gas resistant" would be more accurate. As a further example of this usage, treated animal skins were inaccurately described as "gastight" or "impermeable" in U.S. Pat. No. 1,709,499 and German Pat. No. 227,521. Thus, when the ratio of a balloon's volume to the surface area of its envelope is relatively large, e.g. Volume/Area greater than 0.2 meters (0.7 ft.) and typically greater than 1.5 meters (5 ft.), then the normal diffusion of the lighter than air gas such as helium through the envelope material is negligible in that the balloon can remain buoyant and aloft for several days and even several years and thus fulfill its designed capability. Therefore, the prior art balloon envelope materials discussed in these patents which relate to larger aeronautical balloons are described as impermeable or gasproof even though such materials are not truly impermeable or gasproof.
It is known to use metal powdered coatings on a balloon envelope for the purpose of protecting the envelope from heat and light but not to significantly improve gas impermeability. Disclosures of such coatings are found in German Pat. Nos. 276,717; 286,260; and 262,005. Furthermore, metal layers have been provided on a balloon envelope to improve electrical conductivity such as described in U.S. Pat. No. 1,180,732, or to improve the special characteristics of weather balloons in which an indefinite life is undesirable, as described in U.S. Pat. No. 3,340,732.
Recent developments in aeronautical balloon technology disclosed the use of biaxially oriented plastic film from polyolefins such as described in U.S. Pat. No. 3,608,849. Again, with the large aeronautical balloons with envelopes which have relatively large volume to surface area ratios, it is not necessary to have completely gas impermeable envelopes in order for the balloon to have a very long buoyant lifetime.
Thus, all of the teachings referenced above are concerned with aeronautical balloons which range from weather balloons having a volume approximately 100 cu. ft. to larger balloons intended for practical lifting of men or materials which range in volume from about 2000 cu. ft. to over 1 million cu. ft. The materials disclosed as suitable for such large balloons cannot be scaled down to form suitable toy or advertising balloons which have a volume in the order of 20 cu. ft. or smaller because the increase in surface area in relation to volume of the resulting envelope accompanying such a reduction in size will allow too much of the lighter than air gas to escape through the envelope material.
For example, with a given polymeric envelope material of given permeability and configuration, the buoyant lifetime (T.sub.L) varies in proportion to the square of the linear size (D), e.g., the diameter or radius in the case of a sphere, as defined by the equation T.sub.L .varies.D.sup.2.
Using this common mathematical expression it is readily possible to compare the performance of relatively smaller balloons to that of a hypothetical large spherical balloon having a radius of 62 ft., a corresponding volume of 1 million cubic feet and a reasonable hypothetical buoyant lifetime expectancy of 100 years based on the properties of conventional balloon envelope materials. Such a balloon would correspond in size to a large blimp or dirigible gas bag and its efficiency in terms of buoyant lifetime or rate of helium loss is so great that any further improvement in buoyant lifetime is economically trivial. The choice of this extremely large balloon for a standard is also significant because the relatively thick envelope allows the use of sophisticated complex laminate envelope material which cannot in actual practice be scaled down for a smaller balloon. The scaling down of this balloon to a small blimp having a sphere radius of 36 ft. and a volume of 200,000 cu. ft. will result in a hypothetical buoyant lifetime of 34 years. Further scaling down such balloon to a typical 1 to 4 man sporting balloon having a sphere radius of 18 ft. and a volume of 24,000 cu. ft. results in a hypothetical buoyant lifetime of 8.4 years. Further scaling the large balloon down to a size of a minimum size man lift balloon having a sphere radius of 12 ft. and a volume of 7,000 cu. ft. results in a hypothetical buoyant lifetime of about 3.7 years. To further scale such large balloon down to the size of a toy balloon having a sphere radius of 0.49 ft. and volume of 1/2 cu. ft. results in a hypothetical buoyant lifetime of only about 2.3 days. Thus, it is clear that conventional balloons with relatively long hypothetical buoyant lifetimes, cannot be effectively scaled down using existing balloon envelope technology to yield small balloons having a volume of 20 cu. ft. or less and relatively small volume to surface area ratios but also relatively long buoyant lifetimes.